As to existing four-stroke engines of vehicles, there are generally three working conditions during operation, respectively are: 1, working with full load; 2, gliding; 3, working with middle or little load. Among the three conditions, the first one is the most idealized, but does not occupy a large proportion. As to the second condition, when the vehicle needs no power during gliding, the engine not only does no work but does negative work, which wastes kinetic energy. The third condition has a low efficiency and wastes fuel (according to existing security performance of vehicles, gliding out of gear is prohibited).
Under the first idealized condition, when an existing four-stroke engine operates normally, there is only one stroke does positive work, whereas other three strokes create conditions for the stroke doing the work and do negative works.
Under the second condition, as shown in FIG. 1a to FIG. 1d, the four strokes of the engine are all doing negative work when the vehicle glides, especially for the compressing stroke shown in FIG. 1b. The reason is that, during the compression stroke, an inlet valve 101 and an exhaust valve 102 are both closed, the cylinder is obturated. Thus, a large retarding force is generated. Therefore, it can be seen that the retarding force generated by the compression stroke is the primary reason that the engine wastes kinetic energy and the vehicle does not glide far.
The third condition is easy to be understood and will not be described herein.
By referring to resources such as automobile techniques, automobile structures, Chinese patents CN85200450U, CN86209043U, 93200231.5 and CN87103742A, and by comparing with existing domestic and foreign techniques, it can be seen that prior art generally focuses on how to increase the efficiency of the engine but pays a little attention to how to reduce the waste of kinetic energy of the engine. For example, the variable valve timing technology proposed by Toyota is to make the inlet process more sufficient. The direct injection in the cylinder is to make the burning more complete and ideal. The variable compression ratio technique also belongs to this kind of technique. Although the cylinder closing and emission reduction technique of Mitsubishi can improve the efficiency but it does not decrease the retarding force of cylinder closing. According to the existed technology, the inlet valve and the exhaust valve are closed to reduce cylinder but the retarding force is not decreased. Also, the existed technology has the state that the inlet valve is closed and the exhaust valve is constant opened and has the state that the inlet valve is constant opened. Although it can reduce pressure but cannot ensure the vacuum of an inlet manifold and has deficiencies such as affecting braking of the original vehicle and has a complex structure.